1. Field of the Invention
This invention relates generally to a system and method for determining a virtual target path around an object in front of a subject vehicle and, more particularly, to a system and method for determining a virtual target path evasive steering path around a target vehicle in front of a subject vehicle that uses a potential field process employing a quadratic polynomial function.
2. Discussion of the Related Art
Modern vehicles sometimes include a collision avoidance system that employs object detection sensors that are used to enable collision warning or avoidance and other active safety applications. Various collision avoidance systems and/or adaptive cruise control systems of this type are known in the art that provide automatic vehicle control, such as braking, if a potential or imminent collision with another vehicle or object is detected, and also may provide a warning to allow the driver to take corrective measures to prevent the collision. For example, adaptive cruise control systems are known that employ a forward looking sensor, such as a radar or LiDAR sensor, that provides automatic speed control and/or braking if the vehicle is approaching another vehicle. Also, collision avoidance systems are known that employ sensors for determining if a collision with an object may be imminent that may provide automatic vehicle braking even if the vehicle operator is controlling the vehicle.
The object detection sensors for these types of systems may use any of a number of technologies, such as short range radar, long range radar, cameras with image processing, laser or LiDAR, ultrasound, etc. The object detection sensors detect vehicles and other objects in the path of a subject vehicle, and the application software uses the object detection information to provide warnings or take actions as appropriate. The warning can be a visual indication on the vehicles instrument panel or in a head-up display (HUD), and/or can be an audio warning or other haptic feedback device, such as haptic seat. In many vehicles, the object detection sensors are integrated directly into the front bumper or other fascia of the vehicle.
These types of systems often employ long-range sensors that have a narrow field-of-view in the near-field of the vehicle. Particularly, the sensor signals emanate from a point source on the vehicle and extend in the forward direction of the vehicle, typically to about 150 meters. The collision warning system transmits a radar or laser beam forward of the vehicle and processes reflections from objects in front of the vehicle. The system generates measurements from the reflections and assesses the potential for a collision based on the vehicle's speed, direction relative to the objects, road surface conditions, etc.
Radar and LiDAR sensors that are sometimes employed on vehicles to detect objects around the vehicle and provide a range to and orientation of those objects provide reflections from the objects as multiple scan points that combine as a point cluster range map, where a separate scan point is provided for every ½° across the field-of-view of the sensor. Therefore, if a target vehicle or other object is detected in front of the subject vehicle, there may be multiple scan points that are returned that identify the distance of the target vehicle from the subject vehicle. By providing a cluster of scan return points, objects having various and arbitrary shapes, such as trucks, trailers, bicycle, pedestrian, guard rail, K-barrier, etc., can be more readily detected, where the bigger and/or closer the object to the subject vehicle the more scan points are provided.
Heretofore, collision avoidance systems have generally been limited to systems that provide automatic braking in the event that the vehicle driver does not take evasive action in time to prevent a collision. However, collision avoidance systems of this type may benefit from providing combined automatic braking and steering to avoid a collision.
U.S. patent application Ser. No. 12/908,699, titled, Vehicle Collision Avoidance and Warning System, filed Oct. 20, 2010, assigned to the assignee of this application and herein incorporated by reference, discloses a collision avoidance system that employs combined automated braking and steering. The collision avoidance system defines first, second, third and fourth thresholds that identify a time to collision with a target vehicle by a subject vehicle that are based on the speed of the subject vehicle, the acceleration of the subject vehicle, the speed of the target vehicle, the acceleration of the target vehicle, the distance to the target vehicle from the subject vehicle and a coefficient of friction of the roadway on which the subject vehicle and the target vehicle are traveling, where the first threshold is greater than the second threshold, the second threshold is greater than the third threshold and the third threshold is greater than the fourth threshold. The collision avoidance system determines if the time to collision is less than the first threshold, and if so, initiates a collision warning. The collision avoidance system also determines if the time to collision is less than the second threshold if the time to collision is less than the first threshold, and if so, provides limited automatic braking of the subject vehicle. The collision avoidance system also determines if the time to collision is less than the third threshold if the time to collision is less than the second threshold, and if so, check the condition of whether a roadway lane adjacent to the subject vehicle is clear. The collision avoidance system provides full automatic collision avoidance braking if the time to collision is less than the third threshold and the lane adjacent to the subject vehicle is not clear. The collision avoidance system also determines if the time to collision is less than the fourth threshold if the time to collision is less than the third threshold and the lane adjacent to the subject vehicle is clear. The collision avoidance system provides both automatic steering and braking of the subject vehicle if the time to collision is less than the fourth threshold and the lane adjacent to the subject vehicle is clear.
As discussed above, collision avoidance systems are known in the art for providing automatic steering of a subject vehicle to avoid a slower or stopped object in front of the subject vehicle in the event that the vehicle driver does not take evasive action on his own. The collision avoidance systems provide warnings to the vehicle driver and depending on whether the driver takes evasive action, may provide automatic braking and/or automatic steering. If the system determines that automatic steering is necessary to avoid a collision, the system must calculate a safe steering path for the subject vehicle to provide the steering control. Some of those systems are able to detect lane markings so as to calculate the steering path of the subject vehicle to make a lane change for collision avoidance purposes. Those collision avoidance systems also provide steering commands that cause the subject vehicle to follow the calculated steering path to provide the vehicle steering. For example, U.S. patent application Ser. No. 12/399,317, titled, Model Based Predictive Control for Automated Lane Centering/Changing Control Systems, discloses a system and method for providing steering control for lane changing or lane centering purposes in an autonomous or semi-autonomous vehicle driven system. However, there remains a need to calculate an evasive steering path in these types of collision avoidance systems where lane markings for adjacent lanes are not present for collision avoidance purposes.